A. Short

Readout modes and automated operation of the Swift X-ray Telescope

The Swift X-ray Telescope (XRT) is designed to make astrometric, spectroscopic, and photometric observations of X-ray emission from Gamma-ray Bursts and their afterglows in the energy band 0.2-10 keV. In order to provide rapid-response, automated observations of these randomly occurring objects without ground intervention, the XRT must be able to observe objects covering some seven orders of magnitude in flux, extracting the maximum possible science from each one. This requires a variety of readout modes designed to optimise the information collected in response to shifting scientific priorities as the flux from the burst diminishes. The XRT will support four major readout modes: imaging, two timing modes and photon-counting, with several sub-modes. We describe in detail the readout modes of the XRT. We describe the flux ranges over which each mode will operate, the automated mode switching that will occur and the methods used for collection of bias information for this instrument. We also discuss the data products produced from each mode.

The signature of supernova ejecta in the X-ray afterglow of the |[gamma]|-ray burst 011211

Now that γ-ray bursts (GRBs) have been determined to lie at cosmological distances, their isotropic burst energies are estimated to be as high as 1054 erg (ref. 2), making them the most energetic phenomena in the Universe. The nature of the progenitors responsible for the bursts remains, however, elusive. The favoured models range from the merger of two neutron stars in a binary system to the collapse of a massive star. Spectroscopic studies of the afterglow emission could reveal details of the environment of the burst, by indicating the elements present, the speed of the outflow and an estimate of the temperature. Here we report an X-ray spectrum of the afterglow of GRB011211, which shows emission lines of magnesium, silicon, sulphur, argon, calcium and possibly nickel, arising in metal-enriched material with an outflow velocity of the order of one-tenth the speed of light. These observations strongly favour models where a supernova explosion from a massive stellar progenitor precedes the burst event and is responsible for the outflowing matter.

The Signature of Supernova Ejecta Measured in the X-ray Afterglow of Gamma-Ray Burst 011211

Now that γ-ray bursts (GRBs) have been determined to lie at cosmological distances, their isotropic burst energies are estimated to be as high as 1054 erg (ref. 2), making them the most energetic phenomena in the Universe. The nature of the progenitors responsible for the bursts remains, however, elusive. The favoured models range from the merger of two neutron stars in a binary system to the collapse of a massive star. Spectroscopic studies of the afterglow emission could reveal details of the environment of the burst, by indicating the elements present, the speed of the outflow and an estimate of the temperature. Here we report an X-ray spectrum of the afterglow of GRB011211, which shows emission lines of magnesium, silicon, sulphur, argon, calcium and possibly nickel, arising in metal-enriched material with an outflow velocity of the order of one-tenth the speed of light. These observations strongly favour models where a supernova explosion from a massive stellar progenitor precedes the burst event and is responsible for the outflowing matter.

VIS: the visible imager for Euclid

Euclid-VIS is the large format visible imager for the ESA Euclid space mission in their Cosmic Vision program, scheduled for launch in 2020. Together with the near infrared imaging within the NISP instrument, it forms the basis of the weak lensing measurements of Euclid. VIS will image in a single r+i+z band from 550-900 nm over a field of view of ~0.5 deg2. By combining 4 exposures with a total of 2260 sec, VIS will reach to deeper than mAB=24.5 (10σ) for sources with extent ~0.3 arcsec. The image sampling is 0.1 arcsec. VIS will provide deep imaging with a tightly controlled and stable point spread function (PSF) over a wide survey area of 15000 deg2 to measure the cosmic shear from nearly 1.5 billion galaxies to high levels of accuracy, from which the cosmological parameters will be measured. In addition, VIS will also provide a legacy dataset with an unprecedented combination of spatial resolution, depth and area covering most of the extra-Galactic sky. Here we will present the results of the study carried out by the Euclid Consortium during the period up to the Critical Design Review.

SWIFT XRT Point Spread Function measured at the Panter end-to-end tests

The SWIFT X-ray Telescope (XRT) is designed to make astrometric, spectroscopic and photometric observations of the X-ray emission from Gamma-ray bursts and their afterglows, in the energy band 0.2 - 10 keV. Here we report the results of the analysis of SWIFT XRT Point Spread Function (PSF) as measured during the end-to-end calibration campaign at the Panter X-Ray beam line facility. The analysis comprises the study of the PSF both on-axis and off-axis. We compare the laboratory results with the expectations from the ray-tracing software and from the mirror module tested as a single unit. We show that the measured HEW meets the mission scientific requirements. On the basis of the calibration data we build an analytical model which is able to reproduce the PSF as a function of the energy and the position within the detector.

Performance of the XMM EPIC MOS CCD Detectors

Measurements made during the selection and evaluation of flight CCD detectors for the XMM EPIC MOS cameras have demonstrated near Fano limited resolution at x-ray energies above approximately 3keV. At lower energies some devices exhibit a fractional charge loss which is believed to be due to recombination at the epitaxy/oxide interface. This has been modeled through a Monte-Carlo simulation by assuming that the pinning implant in the etched electrode structure can cause electrons to flow to the front surface, rather than to the buried channel. In spite of this charge loss, spectral response may be characterized using a double Gaussian with residuals of < 5 percent. Quantum efficiency has been measured using a lithium drifted silicon reference detector and these measurements combined with analytical and Monte Carlo simulation, event size ratios and cosmic ray detection, all give a value for the effective depletion depth of 30 to 35 micrometers .

X-ray detection using bulk GaAs

Abstract Bulk GaAs has been investigated as a material for X-ray detection nominally in the 10–100 keV band using Schottky barrier detectors. The devices which were manufactured were investigated with respect to leakage current, charge collection efficiency and X-ray spectral resolution. A leakage current of 7 nA mm−2 at 20°C was measured and was not attributable to surface leakage. The X-ray charge collection efficiency was variable but was as high as 70%, due to defects in the bulk material and was a strong function of detector thickness and applied bias. The imperfect CCE results in degraded spectral resolution, however the work indicates that this type of detector can perform moderate spectroscopy for X-rays of energy > 14 keV, with a measured FWHM of 4.5 keV at 60 keV and 5.5 keV at 122 keV.

Radiation effects on astrometric CCDs at low operating temperatures

Emission times of proton-induced traps and optical spot profiles have been measured at temperatures around -110/spl deg/C for large format charge-coupled devices (CCDs), representative of those to be used for the Gaia mission. There are at least seven trap species involved, with emission times in the range 0.3 /spl mu/s to 130 s and there is evidence for charge re-trapping by fast traps. Trap filling using a charge injection gate is discussed.

The X-ray polarisation sensitivity of CCDs

Abstract The regular array of pixels in a silicon Charge Coupled Device (CCD) may be used to measure photoelectron emission directions following the absorption of high energy X-rays ( E > 15 keV). CCDs offer, therefore, the possibility of combining X-ray imaging and spectroscopy with measurement of the linear polarisation of the incident beam. We describe a simple model of electron transport in CCDs which leads to an estimate of the energy-dependent modulation factor M ( E ) — the parameter determining polarisation sensitivity — for arbitrary pixel geometries. The predictions of the model are in good agreement with published measurements. The sensitivity of an optimised CCD “pixel polarimeter” for cosmic X-ray astronomy is assessed.

The effect of proton damage on the X-ray spectral response of MOS CCDs for the Swift X-ray telescope

The effect of non-ionising energy loss of protons in charge-coupled devices is to displace silicon atoms and any dopant materials present from their lattice positions to form lattice defects which in turn can trap electrons (IEEE Trans. Nucl. Sci. NS-40 (1993) 1628). A CCD operating as a photon counter for X-ray spectroscopy relies on the efficient transfer of charge from one region to another. The number of defects produced will reduce the charge transfer efficiency and hence degrade the spectral resolution of the energy distribution of interest (Jet-X Project Document: JET-X(94) UL-230 WP2220 (1994)). The Swift X-ray telescope will be equipped with a single EPIC MOS CCD22 as developed for the XMM project SPIE 3445 (1998) 13. It is the aim of this study to determine the effect of the radiation environment on the performance of the CCD and its impact on the scientific objective of the X-ray telescope, to probe the X-ray afterglow of gamma-ray bursts.